全文获取类型
收费全文 | 14115篇 |
免费 | 3113篇 |
国内免费 | 3942篇 |
专业分类
测绘学 | 1403篇 |
大气科学 | 2923篇 |
地球物理 | 3375篇 |
地质学 | 7495篇 |
海洋学 | 2156篇 |
天文学 | 623篇 |
综合类 | 1281篇 |
自然地理 | 1914篇 |
出版年
2024年 | 77篇 |
2023年 | 238篇 |
2022年 | 677篇 |
2021年 | 815篇 |
2020年 | 658篇 |
2019年 | 758篇 |
2018年 | 813篇 |
2017年 | 766篇 |
2016年 | 846篇 |
2015年 | 800篇 |
2014年 | 935篇 |
2013年 | 1047篇 |
2012年 | 1063篇 |
2011年 | 1093篇 |
2010年 | 1061篇 |
2009年 | 976篇 |
2008年 | 966篇 |
2007年 | 878篇 |
2006年 | 757篇 |
2005年 | 676篇 |
2004年 | 536篇 |
2003年 | 498篇 |
2002年 | 549篇 |
2001年 | 527篇 |
2000年 | 425篇 |
1999年 | 465篇 |
1998年 | 363篇 |
1997年 | 329篇 |
1996年 | 290篇 |
1995年 | 238篇 |
1994年 | 203篇 |
1993年 | 189篇 |
1992年 | 146篇 |
1991年 | 100篇 |
1990年 | 81篇 |
1989年 | 74篇 |
1988年 | 57篇 |
1987年 | 37篇 |
1986年 | 34篇 |
1985年 | 31篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 10篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1958年 | 5篇 |
1957年 | 4篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Frequency-selective attenuation of sound propagaion and reverberation in shallow waterTXFrequency-selectiveattenuationofsoundp... 相似文献
122.
提出了混合型单调算子对的概念,并给出了其不动点的存在唯一性;研究了它在微分方程组的具体应用. 相似文献
123.
Young-Ok Kim Eun Jin Yang Jung-Hoon Kang Kyoungsoon Shin Man Chang Cheol Soo Myung 《Ocean Science Journal》2007,42(1):9-17
The summer distributions of planktonic microbial communities (heterotrophic and phtosynthetic bacteria, phtosynthetic and
heterotrophic nanoflagellates, ciliate plankton, and microphytoplankton) were compared between inner and outer areas of Lake
Sihwa, divided by an artificial breakwater, located on the western coast of Korea, in September 2003. The semienclosed, inner
area was characterized by hyposaline surface water (<17 psu), and by low concentrations of dissolved oxygen (avg. 0.4 mg L1) and high concentrations of inorganic nutrients (nitrogenous nutrients >36 μM, phosphate <4 μM) in the bottom layer. Higher
densities of heterotrophic bacteria and nanoflagellates also occurred in the inner area than did in the outer area, while
microphytoplankton (mainly diatoms) occurred abundantly in the outer area. A tiny tintinnid ciliate, Tintinnopsis nana, bloomed
into more than 106 cells L1 at the surface layer of the inner area, while its abundance was much lower (103-104 cells L1) in the outer area of the breakwater. Ciliate abundance was highly correlated with heterotrophic bacteria (r = 0.886, p <
0.001) and heterotrophic flagellates (r = 0.962, p < 0.001), indicating that rich food availability may have led to theT. nana bloom. These results suggest that the breakwater causes the eutrophic environment in artificial lakes with limited flushing
of enriched water and develops into abundant bacteria, nanoflagellates, and ciliates. 相似文献
124.
125.
The longitudinal strength of turret mooring productive/storage tanker is studied.A numeri-cal example has been implemented according to the method presented in this paper to give practical il-lustration.From the results of the numerical example,it is concluded that the turret hole located near theforward of the amidships has small effect on the longitudinal strength of the ship hull.As for design ex-treme value of wave bending moment of storage tanker,statistic method is a more reasonablemethodology,especially with the consideration of the servere environmental conditions.The primary esti-mation of design section modulus of turret storage tanker can be determined by this design bending mo-ment. 相似文献
126.
The development of embryos and larvae of Babyloniaformosae habei living along the southeast coast of China is observed under laboratory conditions. The egg masses are laid by females on hard substrate at night and each capsule contains 100-500 eggs. Each egg is 250-280 mm in diameter. The fast two cleavages of the embryo are meridional and equal, and a polar lobe is produced. Larval kidney, which only consists of a single cell, appears during the gastrula stage on each side of the embryo. The right tentacle develops prior to the left one. At 25-27 ℃, an intracapsulate veliger stage is reached about 4.5 d after deposition. The larvae hatch on the fifth day as swimming veligers with a shell length of 360 -500 mm. The newly hatched larva can ingest suspended algal cells from the water column and remains in the pelagic stage for 8-10 d. The newly settled juveniles are 900-1 200 mm in shell length. 相似文献
127.
128.
作者在已完成大气激光雷达系统夜间工作的基础上 ,对白天工作条件下的各种环境背景光的干扰进行了理论与实验分析 ,得出太阳直射光和天空光为白天工作的主要背景干扰。实验结果表明 ,经过激光发射与接收视场角严格匹配及使用干涉滤光器 (2 .6 nm和 0 .15nm)进行窄带滤波 ,背景干扰被明显地剔除 ,可进一步压低背景干扰约 2 0倍。证明采取视场匹配及干涉滤光器的措施可基本保证激光雷达系统在白天条件下工作。 相似文献
129.
130.
1989年对白洋淀重新蓄水后的轮虫作了采样调查,共采到轮虫123种,隶属于46属12科,并对鉴定到种的轮虫作了初步分析。 相似文献